1. Field of Invention
The present invention is directed to precision cut fluid seals, such as for use in any microfluidic device including ink jet print cartridges, and methods for precision cutting such fluid seals. In particular, the present invention is directed to precision cutting methods using a laser cutting source.
2. Description of Related Art
Making a connections between two fluid containing or transporting components is widely practiced. In the new and emerging area of microfluidics, the fluid carrying components are small, in the range of 500 microns down to as small as 1 micron and possibly even smaller. For a general description of this class of devices, see for example, the conference proceedings "Microfluidic Devices and Systems," Proceedings of the SPIE, Vol. 3515 (1998). Microfluidic devices pose challenges in fluid path connection both within the microscopic componentry and also for the connection between a microfluidic device and macroscopic fluid containers or transporters. Such microfluidic devices are important in a wide range of applications that include drug delivery, analytical chemistry, microchemical reactors and synthesis, genetic engineering, and marking technologies including a range of ink jet technologies including thermal ink jet.
In existing thermal ink jet printing, such as disclosed in U.S. Pat. No. 4,774,530, the print cartridge comprises one or more ink filled channels, communicating with a relatively small ink supply chamber or manifold, at one end and having an opening at the opposite end, referred to as a nozzle. A thermal energy generator, usually a resistor, is located in each of the channels, a predetermined distance from the nozzles. The resistors are individually addressed with a current pulse to momentarily vaporize the ink and form a bubble, which expels an ink droplet. As the bubble grows, the ink bulges from the nozzle and is contained by the surface tension of the ink as a meniscus. As the bubble begins to collapse, the ink still in the channel between the nozzle and resistor starts to move towards the collapsing bubble, causing a volumetric contraction of the ink at the nozzle and resulting in the separation of the bulging ink as a droplet. The acceleration of the ink out of the nozzle while the bubble is growing provides the momentum and velocity of the droplet in a substantially straight-line direction towards a recording medium, such as paper. Because the droplet of ink is emitted only when the resistor is actuated, this general type of thermal ink jet printing is known as "drop-on-demand" printing.
U.S. Pat. No. 5,736,998 describes an improved ink seal between a nozzle plate and the pen cartridge in an ink jet printhead. Though mention is made of optimized shape and the use of a dispensed bead of adhesive, no mention is made of a laser cut seal or a discreet fluid seal member.
Another exemplary print cartridge is disclosed in U.S. Pat. No. 4,463,359. The disclosed print cartridge has one or more ink-filled channels, which are replenished by capillary action. A meniscus is formed at each nozzle to prevent ink from weeping therefrom. A resistor or heater is located in each channel upstream from the nozzles. Current pulses representative of data signals are applied to the resistors to momentarily vaporize the ink in contact therewith and form a bubble for each current pulse. Ink droplets are expelled from each nozzle by the growth and collapse of the bubbles. The current pulses to the heater are shaped to prevent the meniscus from breaking up and receding too far into the channels after each droplet is expelled. In addition, various embodiments of linear arrays of thermal ink jet devices are known, such as those having staggered linear arrays attached to the top and bottom of a heat sinking substrate and those having different colored inks for multiple colored printing.
Previously, a typical end-user product in this art was a cartridge in the form of a prepackaged, usually disposable, item comprising a sealed container holding a supply of ink and, operatively attached thereto, a die module having a linear or matrix array of channels. Presently, however, products are designed using a more permanent (or at least multi-use) print cartridge connected to a replaceable ink tank unit. Generally, the cartridge or print cartridge unit may include terminals to interface with the electronic control of the printer; electronic parts in the cartridge itself are associated with the ink channels in the print cartridge, such as the resistors, as well as digital means for converting incoming signals for imagewise operation of the heaters. In one common design of printer, the cartridge is held with the print cartridge in close proximity to the sheet on which an image is to be rendered, and is then moved across the sheet periodically, in swaths, to form the image, much like a typewriter. Full-width linear arrays, in which the sheet is moved past a linear array of channels that extends across the full width of the sheet, are also known. Typically, cartridges are purchased as needed by the consumer and used either until the supply of ink is exhausted, or, equally if not more importantly, until the amount of ink in the cartridge becomes insufficient to maintain the back pressure of ink to the print cartridge within the useful range.
However, in many of the various print cartridge designs, an important feature of the print cartridge is the fluid seal, generally located between the ink supply manifold and the ink drop ejecting die module. The fluid seal is important because it must ensure a tight seal between the ink manifold and the die module. If a tight seal is not maintained, then ink can leak out of the print cartridge through the connection area and/or air and other contaminants can be introduced into the print cartridge and ink supply. A second important function is to seal the ink manifold fluid path in areas adjacent to the die module.
One example of a fluid seal is disclosed in U.S. Pat. No. 5,696,546, which describes an ink cartridge for an ink jet printer, having an ink supply in a housing in fluid communication with an ink supply manifold. The ink is contained in an absorbent material in the ink supply, which has a housing floor having a vent and an ink outlet into a manifold. The manifold is an elongated recess in the outer surface of the housing. There can be a single or multiple chambers connected to a single or multiple ink supplies, depending on whether the print cartridge is a monochrome or multicolor print cartridge. The chamber or chambers in the manifold have a common flat surface. A fluid seal or film member is bonded to this flat surface by an adhesive not attacked or eroded by the ink. This bond between the fluid seal and manifold must prevent ink from leaking from the manifold or ink leaking between chambers within the manifold. There is at least one via or opening that goes all of the way through the fluid seal for each chamber in the manifold. These vias provide fluid communication between each manifold chamber and an inlet of the die module. The surface of the film member opposite the surface bonded to the manifold is coated with a thermosetting adhesive, which bonds to a die module surface containing the ink inlets. The die module ink inlet is of similar size and is aligned with the vias in the fluid seal. The adhesive makes a seal around the via in the fluid seal and the inlet to the die module to provide a fluid communication path between a chamber of the manifold and the inlet to the die module while preventing fluid from leaking out of the desired fluid path. The adhesive bonding the fluid seal to the housing floor is either a pressure sensitive adhesive or the same thermosetting adhesive as is used on the other side of the film member. In this reference, the fluid seal is cut using a die cutting method.
As generally practiced in the art, fluid seals and other parts are cut from multilayer sheet stock using a die cutting process. For an application such as the creation of fluid seals, the shortcomings of die cutting include large design rules, both distortion of the adhesive or other layers near cut edges and long range distortion, the use of lubricants, generation of debris, and difficulty in making controlled-depth cuts.
Design rules for die cut parts will depend on the thickness of the sheet stock. The typical thickness of the multiple layer sheet stock used to make fluid seals is between 250 .mu.m and 500 .mu.m. For these typical sheet stock thicknesses, the minimum dimensions for vias are of the order of 300 .mu.m.times.300 .mu.m, and minimum areas between cuts, such as between two vias or between a via and an edge, is of the order of 500 .mu.m. The relatively large feature sizes and spacing are the result of several factors in the die cutting process. The small via size is related to both distortion of the film created by the mechanical shearing of the cutting die and to the strength of the cutting die with features of such small dimension. The large separation between features is required because the mechanical pressure can distort or in some cases tear the sheet stock between close features. Another type of distortion that requires features to be well separated is displacement of the adhesive near cut edges. This distortion can extend 100 .mu.m to 200 .mu.m from a cut edge. The distortion of the adhesive reduces the ability of this perturbed adhesive to form a fluid-tight bond with either the manifold or the die module. Wide separation of cut features facilitates the formation of fluid-tight bonds in the unperturbed adhesive areas away from the cut edges. Long range distortion is again the result of the mechanical nature of the die cutting process and converts the flat sheet stock to a cut part that is not flat. This can cause additional problems in creating a uniform seal between the manifold and the fluid seal and between neighboring ink inlets of the die module.
Die cutting sheet stock containing one or more thick layers of adhesive can leave adhesive on the cutting tool and cause additional distortion, failure to meet dimensional tolerances or jamming of the die cutting tool. To reduce sticking or to delay its onset, lubricants are frequently used to coat the die-cutting tool. Though the lubricant can be effective in this job, the lubricant can also modify or contaminate the adhesive so that it does not perform as well as the uncontaminated adhesive.
The die cutting process also involves shearing action between two cutters. The shearing action can create plastic fibers and adhesive strings. The larger of the plastic fibers can create a leak path if it is located between the adhesive and sealing surface. The smaller fibers can be carried by ink into the die module and clog the fine jets in the die module or otherwise impede ink flow. The adhesive strings can create difficulties in handling the fluid seal in the assembly equipment for the print cartridge or migrate to the surface of the die module containing the ink exit nozzles and interfere with the operation of the printing.
In forming the fluid seal for inclusion in a manufacturing line for automated assembly of print cartridges, it is convenient to have the fluid seal remain on a carrier tape. This can be done by not cutting through one layer, say the bottom layer, of a multi-layered sheet stock. To cut partially through the sheet stock requires good control of the cut depth. Since the adhesive layers can re-flow, it is important to separate the adhesive on opposite sides of the cut. The shearing action of die cutting can cut through the adhesive layers but, since it does not remove material, the parted adhesive has a tendency to reflow and stick back together. When this happens, the part may be difficult to remove on the manufacturing line or strings of adhesive can interfere with the assembly process. The complications and shortcomings inherent in die cutting of fluid seals presents significant design limitations on an ink jet print cartridge containing fluid seals. The complications in the creation of parts with die cutting leads to significant problems with part yield and with loss of fully assembled print cartridges. Design limitations, process limitations, and both part and print cartridge yield all lead to a significant cost associated with the die cutting process.
Laser cutting and ablation methods are generally known, and have been applied in various methods within the ink jet art as well as in other arts. U.S. Pat. No. 4,049,945 describes a method for cutting different shapes in a moving web by using both the motion of the web and the linear scanning of the laser to be able to cut individual features rather than using step and repeat and encompasses only scanned spot cutting. U.S. Pat. No. 4,639,572 describes the cutting of composite materials such as circuit boards that contain a filler and a polymer matrix and not multi-layer sheet stock. U.S. Pat. No. 5,630,308 describes a method for the scoring of packaging material using a laser such that the scored line is weakened to enable controlled tearing of the material. A process for cutting through several members while leaving one member intact is not described. U.S. Pat. No. 4,549,063 describes using a laser to make discontinuous cuts to provide perforations in an adhesive laminate. The perforations permit tearing labels off of a laminate backing.
Laser cutting methods are also known in the art for forming large parts. For example, laser patterning and cutting methods have been used in many areas, such as sheet metal fabrication, cloth cutting, and paper cutting.
Laser ablation has been used in the ink jet art to form specific features in ink jet die modules, such as ink passageways, orifices, and the like. U.S. Pat. No. 5,208,604 describes an ink jet head wherein the ink discharge opening is formed by laser ablation, i.e., by irradiating an excimer laser onto the discharge opening plate. Similarly, U.S. Pat. No. 5,312,517 and U.S. Pat. No. 5,442,384 disclose forming specific features in an ink jet head using laser ablation methods. However, in each of these patents, none of the cuts form a sealed fluid path between two segments of the print cartridge and the bulk part itself is cut using traditional cutting methods, and the laser is used only for forming features such as holes, lines, and the like.